It is technically difficult to include high levels (e.g., 10-20%) of liquid hydrophobic emollient oil (e.g., sunflower seed oil) and/or hydrophilic liquid humectant (e.g., glycerin) in the form of a solid personal washing bar and meanwhile maintain the bar mildness and benefit delivery to the human skin.
For example, high levels of humectants (e.g., glycerin, low MW polyalkylene glycol) can be trapped in a solid matrix of caboxylic fatty acid soap. However, it is known that carboxylic soap is harsh to skin especially when the soap concentration is high and when the soap is dissolved in the aqueous washing liquor through its own hydrophilic tendency or through the acts of cosurfactants in the bar.
On the other hand, non-soap synthetic bar formulations are primarily structured by either hydrophobic crystalline materials such as free fatty acid or paraffin wax or by hydrophilic crystalline materials such as polyalkylene glycol of high molecular weight (e.g., MW between 2000 and 20000).
Not to be bound by the theory, formulating high levels of emollient oil into the hydrophobic crystalline materials is believed to result in tightly binding the oil with the hydrophobic crystalline structurants. This contributes to the incapability of releasing the oil to water from the bar and may prevent delivering oil to skin via personal wash (see Example 1).
Including liquid oils and/or liquid humectants in bars structured by hydrophilic crystalline materials leads to another difficulty. That is, the oil and the humectant are not compatible with the hydrophilic structurants such as PEG 8000, and this incompatibility results in oil leakage and phase separation from the bulk portion of the bar solid (see Example 1).
Therefore, a novel mild bar structuring system is required to be able to satisfactorily structure the oil and/or the humectant in the bar solid while simultaneously permitting oil release from the bar to the aqueous liquid and then to the human skin via the route of personal wash.
Novel to the art, the applicants of the subject invention found a specific group of polyol esters (i.e., having specific ranges of HLB and specific melting temperature) are capable of both structuring a high level of hydrophobic emollient oils and/or humectants in solid form while still permitting the oil and humectants to be released from the solid into aqueous liquor to be delivered to the human skin through the route of personal wash. Balancing the ratio between polyol ester and oil/humectant are critical to achieve the desired oil structuring and oil releasing. The polyol ester solids containing high level of emollients/humectants can be processed into the form of soft solid chips, flakes or powders and then mixed with "base" chips (comprising the surfactant system) prior to milling, extruding and stamping the bars. This specific way of processing the bars is referred herein as the "adjuvant technology". Using the said specific polyol esters to incorporate high levels of emollients/humectants in the adjuvant chips that are then mixed with the base chips results in novel bar formulations, which are able to deliver high dosage of benefit agents to skin via personal wash and provide satisfactory bar user properties such as cream and/or lotion-like lather even in the presence of high oil levels. The presence of high levels of oil and/or humectant in bar made by said adjuvant technology also effectively reduces the skin irritation potential of surfactants.
The use of polyol esters in personal washing bars is not new.
European Patent Application EP 94105052.8 assigned to Kao Corp. (invented by M. Tonomura and T. Ohtomo), for example, teaches the use of monoglyceridesto boost the lather of formulations comprising only nonionic surfactants. The application does not teach the use of the combination of specific solid monoglycerides and high level of liquid emollient oils/humectants to make bars, preferably pourable, cast melt bars, preferably comprising anionic surfactants and amphoteric surfactants. It does not teach the use of "adjuvant technology" to make high emollient/humectantcontaining bars in general. By contrast, the subject invention found that by using a specific polyol ester (e.g., specific range of HLB, polyol ester to oil/humectant ratio), high levels of emollient oil and/or humectants can be satisfactorily incorporated into adjuvant chips and then mixed with the "base chips" through the adjuvant technology.
An international application published under PCT WO 92/13060 to Procter & Gamble (authored by R. James) teaches the use of monoglycerides in general, PEG and fatty acid as binders for an extruded syndet bar formulation. The prior art, however, does not teach the use of a specific combination of specific monoglycerides (e.g., specific ranges of HLB) and PEG and fatty acid to incorporate high level of liquid emollients (e.g., vegetable oils)/liquid humectants (e.g., glycerin) to make a bar. The prior art also does not teach the specific bar formulation spaces to ensure that high levels of liquid oils and/or humectants can be structured in the solid bar matrixes and can be delivered to skin via personal wash. In contrast, the subject invention uses the adjuvant technology to prepare chips containing high levels of oils and/or humectants. By using a specific polyol ester (e.g., polyol esters with specific range of HLB, specific polyol ester to oil ratio, and specific polyol ester to other structurant (e.g., PEG and fatty acid) ratio), high levels of emollient oil and/or humectants can be satisfactorily incorporated into adjuvant chips and then into bars and can be delivered from the bars to skin under the personal wash condition.
U.S. Pat. No. 5,510,050 to J. Dunbar, P. Beerse, and E. Walker also teaches the use of monoglycerides in general as a non-preferred candidate for the plasticizers in an extruded cleansing bar containing liquid polyols (4-15%) and magnesium soap (4.5 to 50%). The preferred plasticizers are fatty acids, sodium soap, and paraffin wax (Column 5, line 22-24). The prior art, however, does not teach the use of a specific combination of specific monoglycerides (e.g., specific ranges of HLB) and other plasticizers to incorporate high level of liquid emollients (e.g., vegetable oils)/liquid humectants (e.g., glycerin) into a bar. The prior art also does not teach the specific bar formulation spaces to ensure that high levels of liquid oils and/or humectants can be structured in the solid bar matrixes and can be delivered to skin via personal wash. In fact, as found by the subject invention, the preferred plasticizers used in the prior art hinder the skin deposition of liquid oils from bars to skin. The prior art has to use magnesium soap as the key ingredient to aid processing (column 2, line 26). In contrast, the subject invention uses the adjuvant technology to prepare solid chips containing high levels of oils and/or humectants. By using a specific polyol ester (e.g., polyol esters with specific range of HLB, specific polyol ester to oil ratio, and specific polyol ester to other structurant (e.g., PEG and fatty acid) ratio), high levels of emollient oil and/or liquid humectants can be satisfactorily incorporated into chips and then into bars and can be delivered from the bars to skin under the personal wash condition. In the subject invention, carboxylic acid soap is not included in the chip composition and is an optional ingredient of the total bar composition.
A Great Britain Patent GB 1,570,142 assigned to GAF Corp. teaches the use of both hardened triglycerides and fatty alcohols as the plasticizers in an extruded syndet formulation. In contrast to the subject invention, the application does not teach the use of the combination of specific monoglycerides and high level of liquid emollient/humectants to make bars. It does not teach the use of adjuvant technology to make high emollient/humectant containing bars in general. By contrast, the subject invention found that by using a specific polyol ester (e.g., specific range of HLB, polyol ester to oil ratio, and polyol ester to other structurant ratio), high levels of emollient oil and humectants can be satisfactorily incorporated in the bar for the skin benefit through the adjuvant technology.
The art of using the adjuvant technology to incorporate emollients into bars is not new.
U.S. Pat. No. 5,154,849 to Visscher et al. teaches bar compositions containing a silicone skin mildness/moisturizing aid component. In one embodiment, the silicone component may be mixed with a carrier which is selected to facilitate incorporation of the silicone. At column 16, the reference describes that silicone is mixed into melted Carbowax (i.e., polyethylene glycol), that the mixture is cooled to form flakes, and that the flakes are preferably added to an amalgamator.
It is clear, however, that the Visscher et al. contemplates a silicone/carrier system different from the adjuvant chips of the subject invention. First, the Visscher patent does not teach selecting a carrier having specific HLB to both carry high levels of oils and permit oil release from the solid into water. For example, polyethylene glycol (HLB&gt;18) is not miscible with most of hydrophobic oils such as silicone oil or vegetable oil at mixing temperatures (e.g., 70-120.degree. C.), and upon cooling, oil tends to leak out of the PEG solid matrix. Therefore PEG has a poor oil-carrying capacity although it permits oil release from oil into water and then to skin via personal wash (see Example 1). On the other hand, fatty acid, ethers, alcohols or paraffin wax (HLB&lt;2) have high oil carrying capability (Example 1); however, it is difficult to have oils released from those hydrophobic solids into water and then to skin at conditions relevant to personal wash. Novel to the art, subject invention found that specific solid polyol esters (i.e., specific HLB between 2.5 and 15) are capable of carrying high levels of oil/humectant and simultaneously providing oil release from the solid into water then to skin via personal wash.
U.S. Patent applications filed by Unilever (95-R385-EDG and 95-R385-B-EDG) use additional thickeners such as fumed silica or additional hydrophobically modified polyalkylene glycols or EO-PO copolymers to improve the oil-carrying capability of polyalkylene glycol in the adjuvant chips and to modify the dissolution speed of the adjuvant chips in water. Nevertheless, those applications use highly hydrophilic materials such as PEG and EO-PO (HLB&gt;&gt;15) and do not teach selecting a carrier having specific HLB (between 2.5 and 15, preferably between 2 and 8) to not only carry high levels of oils but also permit oil release from the solid into water. For example, polyethylene glycol (HLB&gt;18) or hydrophobically modified PEG claimed (HLB&gt;15) are not miscible with most of hydrophobic oils such as silicone oil or vegetable oil at mixing temperatures (e.g., 70-120.degree. C.), and, upon cooling, oil tends to leak out of the solid matrix (see Example 1). Thus thickeners such as fumed silica have to be added to improve the adjuvant's oil-carrying capacity. Nevertheless, fumed silica is in the form of very fine powders (i.e., 7-30 millimicrons), which increase the processing difficulties and potentially increase the cost. By contrast, subject invention teach the use of specific solid polyol esters (i.e., specific HLB between 2.5 and 15) to carry high levels of oil/humectant and provide oil release from the solid into water then to skin via personal wash without or with a reduced level of thickeners such as fumed silica (e.g., 0-0.5%), which is advantageous because potentially processing can be simplified and cost can be reduced.
In summary, none of the references, alone or in combination teach that the use of specific polyol esters (e.g., having specific melting temperature, especially specific hydrophobic-lipophobic balance (HLB)) in specific adjuvant chips, flakes or granules or powders (i.e., containing greater than or equal to 5% hydrophobic emollient oils and/or humectants in the adjuvant chips, the polyol ester to oil/humectant ratio greater or equal to 1:1, and the polyol ester to other structurant ratio greater than 1:1) will result in bars, processed by adjuvant technology, with enhanced oil/humectant carrying and releasing capabilities. These capabilities are crucial to benefit delivery to the skin via personal wash.
Not to be bound by the theory, it is believed that the adjuvant chips of the subject invention entrapped emollient oils by a mechanism that is different from those of prior art. That is, hydrophobic oils such as sunflower seed oil tend to be miscible with said polyol esters during mixing (temperature between 65-120.degree. C.) to form an one phase isotropic liquid. Upon cooling, the oil may not be in the form of discrete droplets as is found in the adjuvant chips where polyalkylene glycol is the major carrier. Instead, oils may exist in the crystalline cracks or even in the form of solid solution in the chips of the subject invention. The chemical affinity of oil and polyol ester is believed to contribute significantly to the stability of the oils in the polyol ester carrier.